Primary sensory axons injured by dorsal root injuries fail to regenerate into the spinal cord, leading to chronic pain and permanent sensory loss. The mechanisms that prevent regeneration at the CNS-PNS interface, the dorsal root entry zone (DREZ), are unknown. The present approaches for overcoming this regeneration failure have had only limited success. Over the past few years, we have pioneered in applying in vivo imaging to directly monitor sensory axons arriving at the DREZ in living mice. These studies lead us to hypothesize that the regeneration failure and the limited success with current interventions might be because regenerating axons undergo rapid and aberrant synaptic differentiation that causes growth to cease prematurely at the DREZ. To test this idea, we will apply advanced techniques, including in vivo imaging, inducible transgenic mice, and targeted electron microscopy. In Aim 1, we will identify postsynaptic mechanisms by testing whether NG2 glia induce presynaptic differentiation and/or growth arrest. In Aim 2, we will identify presynapti mechanisms by testing whether targeting calcium channel alpha2delta subunits and their interaction with thrombospondins will promote regeneration. In Aim 3, we will promote robust regeneration by combining treatment with gabapentin (GBP) and pregabalin (PG), which prevent synaptogenesis, with conventional interventions targeting intrinsic and extrinsic growth barriers, which individually elicit little regeneration. The proposed work has the potential to revise the prevailing explanation for the regeneration failure of primary sensory neurons and may also be applicable to spinal cord injury. In addition, GBP and PG are commonly prescribed anti-neuropathic pain medications already approved by the FDA. Our work therefore can be quickly applied to patients with brachial plexus, lumbosacral plexus and cauda equina injuries, which are common and debilitating and have no effective treatment.